I have an outside fish pond with goldfish and shubunkans. I have had the pond and the fish for about 20 years. I have noticed some black fish that are about the size of my finger. But I have never seen one grow as big as the other fish. Some of the larger fish are about 10 inches long.Do the black fish change color and is this why I never see any large black fish?I have black ones every year.Thanks if you can help